Process for suppressing deposit formation in an internal combustion engine



United States PatentO PROCESS FOR SUPPRESSING DEPOSIT FORMA-' TION IN AN INTERNAL COMBUSTION ENGINE Robert Y. Heisler and Stanley R. Newman, Fishkill, and Norman Alpert, Poughkeepsie, N.Y., assignors to Texaco Inc., a corporation of Delaware No Drawing. Filed Oct. 19, 1956, Ser. No.'616,917 2 Claims. (Cl. 44-70) This invention relates to an engine lubricating oil containing a novel group of additives which act to control deposits in the combustion zone and to minimize the effects of deposits resulting from the combustion of the fuel, particularly under low temperature conditions. More specifically, this invention discloses that superior lubricating oils, from the standpoint of suppression and removal of low temperature deposits, are obtained by the addition thereto of a minor amount of a compound selected from a prescribed group of aromatic esters.

The need for superior deposit inhibitor additives for engine lubricants is continually increasing due to advances in engine design. All engines in continuous operation eventually suffer from the effect of engine deposits; However, engines which are run at low temperatures usually develop deposits more quickly than those run at higher temperatures.

.Low temperature deposits are of particular concern to automotive owners and operators who run their automobile engines for a period of time and then allow the engines to cool before restarting. For instance, taxicabs and autos used for short delivery runs, particularly in the winter season in colder climates, are subject to low temperature deposits on the engine parts. There are two avenues by which this problem can be attacked. One approach is through the fuel and the other approach is through the lubricating oil. In our co-pending application filed of even date Serial No. 616,915, it is disclosed that superior hydrocarbon motor fuels, from the standpoint of engine deposits, result from the incorporation of an aromatic carboxylic acid ester. The present invention involves the discovery that addition of these aromatic esters to a lubricating oil produces a lubricant marked by the ability to maintain a clean engine even with dirty fuels and under low temperature conditions of operation.

In accordance with the present invention an improved engine lubricant composition which suppresses the formation of engine deposits comprises a major portion of an oleaginous lubricating base fluid and a minor portion sufiicient to suppress deposits in the engine of an aromatic carboxylic acid ester selected from the group consisting of a dibenzoate of a polyethylene glycol having the following general formula:

where n ranges from 2 to 12, preferably 4 to 8, and an Patented Oct. 18, 1960 formula:

where n ranges from 1 to 5, preferably 1 to 2, R is an alkyl group having from 1 to 6 carbon atoms and the carbon to oxygen weight ratio of the phthalate compound does not exceed 2.25, preferably 2.0. In order to maintain the carbon to oxygen weight ratio below 2.25, longer chain terminal radicals are combined with a larger number of repeating ethylene oxide units while lower molecular weight terminal aliphatic radicals are combined with either single or a smaller number of repeating ethylene oxide radicals.

Examples of the alkoxyalkyl phthalates which are use-' ful in accordance with this invention include bis(diethoxyethyl) phthalate more commonly called di-Carbitol phthalate, bis(ethoxyethyl) phthalate commonly called di-Cellosolve phthalate, bis (methoxyethyl) phthalate, bis(methoxy tri-ethoxy ethyl) phthalate and bis(pentaethoxyethyl) phthalate. The preferred phthalates are di- Carbitol phthalate and his (methoxyethyl) phthalate. I

The aromatic esters of the present invention are generally incorporated in the lubricant composition in amounts ranging from 0.25 to 5.0 volume percent. The preferred additive amount, however, ranges from about 1.0 to 3.0 volume percent in the lubricant base.

This invention also contemplates a process for maintaining an internal combustion engine free from deposits, particularly those formed during low temperature operation, by the presence of a compound selected from the above prescribed group of aromatic esters, in the combustion zone. This can be eifected by using a fuel containing the additives of this invention as disclosed in the afore-mentioned copending application, by using a lubrioant containing the additive of the invention as described herein, by employing a fuel and lubricant, both of which contain the additive of this invention, or by the addition of the additive of the invention to either the fuel lubricant, or both during engine operation. In the latter mode of operation, the additive is added to the fuel in an amount to constitute 0.01 to 1 volume percent of the fuel and/or to the lubricant to continue 0.25 tov 5 volume percent of lubricating oil.

A lubricating oil composition of this invention is effective in maintaining deposits at a low level with the result that surface ignition in all its manifestations, mainly preignition and knock, is minimized to a surprising degree. In addition, the low deposits level reduces the engines octane requirement. Deposits on surfaces contacted by the additive-containing lubricating oil, such as piston skirts and cylinder walls, are very markedly reduced.

The aromatic esters in accordance with this invention are effective in controlling deposit formation in lubricants employed in spark ignition engines, diesel motors, and gas turbines. However, these fatty acid esters are normally used in motor oils for spark ignition engines wherein fuel derived deposits formed during low tem-. perature operation are a particularly vexing problem- Diesel lubricants containing the esters of thisinvention'; are effective in eliminating deposits resulting from the use of so-called economy diesel fuels, i.e., fuels having a high sulfur content or containing cracked or residual stocks. The additives of the invention are also useful as deposit-control additives in gas turbine lubricants which are generally ester base compositions. The additives are useful in aviation oils which lubricate reciprocating type aviation engines. The scope of the lubricating oil compositions of the engine is broad and includes mineral oils, synthetic lubricating oils, and mixtures thereof as the base fluids.

The hydrocarbon mineral oils usable in this invention can be paraflin base, naphthene base or mixed parafiinnaphthene base distillate or residual oils. Paraifin base distillate lubricating oil fractions are used in the formulation of premium grade motor oil such as are contemplated in this invention. The lubricating base generally has been subjected to solvent refining to improve its lubricity and viscosity temperature relationship as well as solvent dewaxing to remove waxy components and improve the pour of the oil. Broadly speaking, mineral lubricating oils having an SUS viscosity at 100 F. between 50 and 1,000 may be used in the formulation of the improved lubricants of this invention but usually the viscosity range falls between 70 and 300 at 100 F.

The mineral lubricating oils to which the prescribed group of aromatic carboxylic acid esters of this invention are added usually contain other additives designed to impart other desirable properties thereto. For example, V.I. improvers, such as the polymethacrylates are normally included therein as are materials which act as detergents and dispersants for the removal of combustion chamber deposits. The detergent additives, such as basic barium sulfonate and barium alkyl phenolate, provide the required dispersing properties.

The V1. improver normally used is a polymethacrylate of the general formula:

(IHa CHi.C-

COOR

wherein R is an aliphatic radical ranging from butyl to stearyl and n is an integer having a value of more than 1.

The most commonly used detergent-dispersant additive is an alkaline earth metal sulfonate such as calcium petro leum sulfonate or barium petroleum sulfonate. These products are so well known as detergent-dispersant additives they require no further description. Similarly, divalent metal alkyl phenolates are widely used as detergents either alone or in combination with the alkaline earth metal petroleum sulfonate.

The most commonly used inhibitor and anti-oxidant is a divalent metal alkyl dithiophosphate which results from the neutralization of a P S -alcohol reaction product with a divalent metal or divalent metal oxide. The most widely used inhibitors are barium and zinc alkyl dithiophosphates.

The synthetic lubricating oils are usually of the ester or ether type. High molecular Weight, high boiling liquid aliphatic dicarboxylic acid esters possess excellent viscosity-temperature relationships and lubricating properties and are finding ever increasing utilization in lube oils adapted for high and low temperature lubrication; esters of this type are used in the formulation of jet engine oils. Examples of this class of synthetic lubricating bases are the diesters of acids such as sebacic, adipic, azelaic, alkenyl-succinic, etc.

Polyester lubricants formed by a reaction of aliphatic dioarboxylic acids of the type previously described, a glycol, a monohydroxy alcohol, or a monocarboxylic acid are also employed as the synthetic lubricating base oil. In addition, polyalkylene ethers as illustrated by the polyglycols are useful base fluids. The sulfur analogs of the above-described diesters, polyesters, and polyalkylene 4 ethers are also included as synthetic base fluids for the compositions of this invention.

The action of the dibenzoates and alkoxyalkyl phthalates of the invention in improving the deposit removing properties of a lubricating oil was demonstrated by a Modified Chevrolet Deposits Test CRC-FL-2-650. The laboratory engines were operated under the standard conditions of this test with the exception that crankcase oil temperatures were 10 F. lower, the water jacket temperatures were 5 F. lower, and the crankcases of the test engines were ventilated. These modifications were in every case in the direction of making the test more severe and were intended to simulate low temperature conditions wherein deposit formation is most pronounced. After the termination of each run, the engine was disassembled and its parts were evaluated by a merit system adayted from the CRCL-4-1252 test. This merit system involved visual examination of the engine parts in question and their rating according to deposits by comparison with standards which have been assigned ratings. For example, a rating of 10 on a piston skirt designated a perfectly clean piston while a rating of zero represented the worst condition. Similarly, a rating of on total engine deposits represented a perfectly clean engine, etc.

The following table shows the results obtained in a number of runs using the Modified Chevrolet Deposits Test with lubricating oils which contained various concentrations of the dibenzoates of polyethylene glycols wherein the glycols varied in average molecular weight. The concentration of the dibenzoates in the lubricant was determined by analysis at the termination of the run. The engine tests were run using a fuel which had an 87.0 ASTM research octane rating containing 2.90 ml. of tetraethyl lead per gallon. The fuel had an API gravity of 58.0 and a boiling range between 106 and 396 F. It was negative in the corrosion test and had an oxidation stability in the ASTM test of 530 minutes minimum. The fuel also contained minor amounts of inhibitor compounds, namely, N,N-di-secondary-butyl-p-phenylene diamine, lecithin, and N,N-disalicylidene-1,2-diarnino propane.

The base oil was a 20-20W heavy duty oil meeting supplement I requirements. The reference oil contained a methacrylate V.I. improver and a balanced combination of additives which impart detergent, dispersant, and anti-oxidant properties to the oil. The additive mixtures comprised a barium petroleum sulfonate and a zinc alkyl dithiophosphate in which the alkyl group is a methylcyclohexyl.

TABLE I Chevrolet deposits test results Concentration of Additive in Oil at Run Termination, Vol. Percent Piston Skirt Deposits Total Engine Deposits Base Oil Base oil plus additive:

DE G-dibenzoate PE G-200dibenzoatc PE G-200-dibenzoate PE G-200-dibenzoate- PE G-300-dibenzoate PE G-300-dibenzoate DEG=diethylene glycol. PEG 200; 300=p01yethylene glycol having molecular weights or 200 and 300, respectively.

position used in this test were those previously described as used in connection with the results shown in Table I.

TABLE II Chevrolet deposits tests results Concentra- Carbon Piston Total tion of Adto Oxy- Skirt Engine ditive in gen Wt. De- De- Oil at Run Ratio of posits posits Termina- Additive tion, Vol.

Base oil 6. 1 80. 1 Base oil plus additive:

di-Oarbitol phthalate. 9. 2 85. 2 1 1. 87 dl-Cellosolve phthalate 7. 7 84. 7 3 2. 0 bis(methoxyetl1yl) phth ate 1..1.). ..1. .t ..1.. 8 5 86.5 3 1.75 bis butox e y p a asteuuj 4 8 77.8 3 2.5

invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for suppressing deposit formation in an internal combustion engine which comprises introducing a polyethylene glycol dibenzoate having the following general formula where n ranges from 2 to 12 into the combustion chamber of said engine during operation thereof in an amount sufficient to suppress deposit formation in the engine.

2. A process as described in claim 1 where the polyethylene glycol dibenzoate is derived from a polyglycol having an average molecular weight of about 200 to 300, in an amount ranging from 1 to 3 volume percent of the lubricant employed in said internal conduction engine.

References Cited in the file of this patent UNITED STATES PATENTS Katz et al June 25, 1946 Morris et al Jan. 6, 1953 

1. A PROCESS FOR SUPPRESSING DEPOSIT FORMATION IN AN INTERNAL COMBUSTION ENGINE WHICH COMPRISES INTRODUCING A POLYETHYLENE GLYCOL DIBENZOATE HAVING THE FOLLOWING GENERAL FORMULA 